Variation

Question 1

what is variation?

Answer 1

variation is the differences between individuals - it is important for evolution to occur

Question 2

what are the two characteristics of variation?

Answer 2

genetic and environmental (there can be a combination of both?

Question 3

what is genetic variation?

Answer 3

following sexual reproduction, or mutation, organisms will have different versions of genes to another individual

Question 4

what is environmental variation?

Answer 4

the environment might also affect the characteristics of an organism

Question 5

what is variation when it is both genetic and environmental?

Answer 5

usually both genetic and environmental factors contribute to the variation found in individuals of a species

Question 6

what are the two main types of variation?

Answer 6

continuous and discontinuous

Question 7

what is continuous variation?

Answer 7

where there is a smooth range of measurements e.g. height

Question 8

what is discontinuous variation?

Answer 8

where there are distinct categories with no values in between e.g. blood group

Question 9

who is Gregor Mendel?

Answer 9

• in 1860 an Austrian Monk called Gregor Mendel noticed that peas in the kitchen garden were of two types: tall and dwarf
• he allowed the tall ones to self-pollinate for a number of generations and did the same with the dwarf ones
• he then assumed that both types were pure breeding
• he then crossed a tall pea plant with a dwarf pea plant

Question 10

what was Gregor Mendel’s method to breed pea plants?

Answer 10

1. he opened up the flowers of the tall plants when they were just emerging and cut out the stamens, the male reproductive parts
2. this would stop the pea plant from self-pollinating
3. he then covered the rest of the flower with a bag to stop insects pollinating the carpel, the female part, with pollen from an unknown source
4. when the flowers from a dwarf variety were ready he removed some pollen from one of the stamens with a very fine paintbrush and brushed it onto the stigma of a carpel protected by the bag

Question 11

what was the results of George Mendel’s plant experiment?

Answer 11

1. the flower produced seeds and when these had dried out properly he planted them to see what was produced
2. all of the seeds grew into tall plants, even though half of the parents were dwarf plants - he allowed these plants to self-pollinate
3. surprising tall parents gave some rise to dwarf plants
4. when the offspring were counted he found that 839 were tall and 276 were dwarf - he realised that this was a ratio of 3 tall plants to 1 dwarf

Question 12

what is an allele?

Answer 12

a version of a gene

Question 13

what are homozygous alleles?

Answer 13

both chromosomes have the same allele (tt and TT)

Question 14

what are the two types of allele?

Answer 14

dominant and recessive

Question 15

what is a dominant allele?

Answer 15

a dominant allele only needs one allele present to be expressed

Question 16

what is a recessive allele?

Answer 16

a recessive allele needs two alleles to be present to be expressed

Question 17

what is a heterozygous allele?

Answer 17

when both contain the one of each allele (Tt and Tt)

Question 18

how can we quickly work out the probability of offspring?

Answer 18

by using a punnet square - gametes for each parent are place in the first column and top row

Question 19

what are the rules of working out genetic crosses?

Answer 19

• use one letter to represent a gene
• use the upper case to represent the dominant allele and the lower case to represent the recessive allele
• write the genotypes (allele combination) and phenotypes (characteristic) of the parents
• write the alleles found in each gamete (separately to the parents’ genotypes)
• write the genotype and phenotype of each offspring
• finish with the probability of each phenotype in the offspring

Question 20

what is polygenic inheritance?

Answer 20

when characteristics are controlled by several genes which influence each other

Question 21

what is cystic fibrosis?

Answer 21

• a disease that effects the lungs
• it affects the CFTR protein which causes mucus to be incredibly thick, so thick that it cannot be removed the lungs
• this can reduce life expectancy by up to 30 years
• there is currently no cure

Question 22

what are carriers?

Answer 22

• when there is a cross between two heterozygous parents
• as the faulty gene is recessive, the parents do not have the disease but do carry an allele

Question 23

what is codominance?

Answer 23

when there are three phenotypes possible even though there are only two alleles

Question 24

what do pedigree diagrams show?

Answer 24

the probability of inheriting a genetic disease

Question 25

what do pedigree diagrams not show us?

Answer 25

whether they are carriers of the disease or if the disease is recessive or dominant (but this can be worked out)

Question 26

how can we work out if a disease was dominant or recessive using a pedigree diagram?

Answer 26

• if the parents are not affected but had an affected child, the child must have inherited one allele from each parent
• if the disease was dominant and the parents had just one copy of the faulty allele they would be affected
• therefore, the disease is recessive

Question 27

what pair of chromosomes determines the sex of a baby?

Answer 27

the 23rd pair

Question 28

what are the chromosomes for male and female?

Answer 28

male = XY
female = XX

Question 29

what is the likelyhood of having a boy or girl?

Answer 29

50:50